Re: Maglight LED retrofit

On 3 Dec 2005 16:37:57 -0800, "Too_Many_Tools"
<too_many_tools@xxxxxxxxx> wrote:

>My understanding from the flashlight review site is that this unit
>using a resistor to limit current.

Using "a" resistor for several paralleled LEDs is bad design, though
most multi-LED flashlights work that way. Multiple LEDs should
either be connected in series so they all get the same current
regardless of their various individual fwd voltage drops, or they
should each have their own dropping resistor. There's no efficiency
penalty in using individual resistors and resistors only cost a penny
or two each though they do need additional board space -- like .060 x
..030 each plus a little for connecting traces, oh dear.

Running in series from batteries requires voltage boost. There
are a number of chips designed and marketed to do exactly that, but
you certainly won't find them in a cheap light -- though the chips
cost less than a buck.


>
>I don't think the flashlight has been used a total of five minutes.
>
>The batteries are normally removed after each short use. They were left
>in overnight and the next day I had a heck of a mess to clean up.

Might those have been the batteries that came with the light? Some
of those are very cheap LeClanche cells, 40's throwbacks.
>
>The two LEDs that have quit look quite different from the others...I
>think they have separated from the potting material which would be a
>symptom of a thermal problem.
>
>Considering that this flashlight was supposed to "last a lifetime", it
>has been one of the most troublesome flashlights I have ever owned.
>
>Anybody else have LED flashlights fail on them?

I have three cheapo ($6.00) 8-LED 3-AAA wonders and I sent Fitch a
bunch of them about a year ago. I've had one eat an LED, haven't
heard that any of Fitch's failed -- though I think he gave most of 'em
away as xmas gifts so who knows. None of my Luxeon lights have
failed.


.

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